1. Field of the Invention
This invention relates to optical sensor arrangements. More specifically, this invention relates to sensor arrangements used within optical imaging systems.
While the present invention is described herein with reference to a particular embodiment, it is understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional embodiments within the scope thereof.
2. Description of the Related Art
Scanning optical systems typically have a mirror or imaging device attached to a scanning member. The mirror reflects incident energy onto optical elements which in turn focus the energy onto a linear array of photodetective elements. In infrared systems the photodetector array is typically cooled to reduce parasitic thermal noise and to thereby increase the sensitivity thereof. The photodetector array and associated cooling apparatus are typically mounted in an evacuated chamber often termed a "dewar". In this manner, electromagnetic energy collected from each region within the scene is used to construct a composite image.
In conventional infrared scanning sensors, the photodetector array is generally designed to be optimally sensitive to radiation within a band of wavelengths. Accordingly, when it is desired to detect radiation from more than a single band, it is necessary to employ an additional photodetector array. In such a "two-color" sensor, radiation reflected by the scanning mirror is typically incident on a beamsplitter. The beamsplitter then redirects radiation of each color to separate focusing arrangements, which focus radiation of each color on photodetector arrays located in separate focal planes. However, the photodetector arrays are mounted within separate dewars and require separate cooling systems as well as separate intervening focusing optics. Two-color sensor systems are therefore considerably more bulky, heavy, complex and expensive than those confined to a single wavelength band.
In addition, the signal-to-noise ratios of images produced by scanning sensors are typically somewhat limited.
Staring sensors employ two-dimensional photodetector arrays. Radiation from the entire field of view of the sensor is simultaneously incident on the detector array. While the signal-to-noise ratios of images produced by staring sensors are typically better than those generated by "scanning" sensors, two-color staring sensors exhibit the disadvantages mentioned above with regard to two-color scanning sensors. That is, a two-color staring sensor also requires a pair of photodetector arrays, a pair of dewars with associated cooling apparatus, and a pair of focusing arrangements. The relatively large volume required by a pair of two-dimensional photodetector arrays with associated focusing optics tend to limit the utility of two-color staring arrays in applications requiring small sensors.
Hence, a need exists in the art for a small, lightweight, low cost two-color staring sensor.